The invention relates to an apparatus for stripping away a punched grid, pushing out an internally formed part and ejecting a blanked part in a precision blanking press, comprising a knife-edged ring cylinder disposed in the top, a knife-edged ring piston for generating a knife-edged ring force that acts on knife-edged ring pins being guided in said cylinder and optionally pressurized by hydraulic fluid by way of a pressure chamber, a main cylinder disposed in the base, a main piston/ram with a counterstay piston that acts on pressure pins to generate a counteracting force being guided in said main cylinder and optionally pressurized by hydraulic fluid through a pressure chamber, said main piston/ram making a stroke movement in the direction of the stroke axis and supporting a table top, and a hydraulic system for supplying the pressure chambers disposed in the top and base with the hydraulic fluid, the fluid being adjusted to a predetermined working pressure by way of a central control system.
The invention further relates to a method for stripping away a punched grid from the blanking punch, pushing out an internal shape and ejecting a blanked part from the die block of a die in a precision blanking press with an upwardly-moving main piston disposed in the base, wherein, firstly, a knife-edged ring force for pressing the knife-edged ring into the material to be blanked is generated using a knife-edged ring piston disposed in the top of the press, said force acting on a guide or knife-edged ring block by way of knife-edged ring pins, and a counteracting force directed opposite to the blanking is generated using a counterstay piston disposed in the base, whereupon the hydraulic fluid is displaced from the pressure chambers of the knife-edged ring or counterstay piston at an adjustable pressure during blanking, and after blanking the pressure chamber of the knife-edged ring piston in the top and the pressure chamber of the counterstay piston in the base are pressurized by a hydraulic fluid from a hydraulic system, the fluid being set to a predetermined working pressure, the pressure chambers being set, using a central control system, to a predetermined stripping/pushing force which strips the punched grid and pushes out the internally formed part, and to a predetermined ejection force which ejects the blanked part.
Precision blanking and the methodology thereof has been known for a long time. The characterizing methodological features include the design of the die, the knife-edged ring, the punch clearance and the acting forces. The precision blanking die comprises an upper part and a lower part. The upper part includes at least one guide or knife-edged ring block which is acted upon by a knife-edged ring force generated by a knife-edged ring piston of a precision blanking press by way of pressure pins, a blanking punch for blanking out a blanked part from the material to be blanked, the punch being guided in the guide or knife-edged ring block, and a pusher for pushing out an internally formed part from the punch. The bottom part contains a die block or matrix, and an ejector guided in the punch, the ejector being acted upon by a counterforce generated by a counterstay piston of the precision blanking press by way of pressure pins, the counterforce counteracting the punch. The material to be blanked is clamped between the guide or knife-edged ring block and the die block. At the beginning of the blanking process, the knife-edged ring located in the guide or knife-edged ring block is pressed into the material to be blanked through the force of the knife-edged ring. Upon subsequent blanking, this force is displaced by the upwardly-moving main piston, and strips away the punched grid from the punch after the blanking is finished, and pushes out the inner shape into the opened interior space of the die. At the beginning of blanking, the counterforce generated by the counterstay piston presses against the punch and is exceeded by the punching force. At the end of the blanking process, this force ejects the blanked part pressed into the die block into the interior of the die (“Umformen and Feinschneiden, Handbuch für Verfahren, Werkstoffe, Teilgestaltung” (Forming and Precision Blanking, Handbook on Methods, Materials, Part Design), pg. 141-153, Verlag Hallwag AG, 1997).
The precision blanking process requires three special triple-acting presses which operate upward from below and which provide controlled regulation of the blanking process, with ancillary functions for the knife-edged ring, the counterstay and the ejector. The forces of the knife-edged ring and counterstay are hydraulically generated and the punching force is mechanically or hydraulically generated.
There are a number of piston arrangements that can be used in presses to drive the process or to apply pressure.
DE 1 145 115 discloses a triple-acting hydraulic press with a working cylinder, an annular piston surrounding the same, a counterpiston and an intermediate chamber disposed between the working piston and the annular piston, the intermediate chamber being able to be blocked off using a pressure regulating valve.
DE 1 279 622 A1 describes a precision stamping press with a punch piston, a pressing piston for pressing the sheet workpiece against the press table and a counterpressure piston for supporting the part to be stamped out from the workpiece, wherein the punch piston is guided in the pressing piston in spring-activated fashion.
DE 1 930 398 A1 4471 discloses a press, in particular for precision stamping, comprising two ram systems to which half of a die is fastened, respectively. At least one ram system comprises two independently actuated piston systems, either of which can be individually selected at the press frame.
The prior art according to DE 2 218 476 A1 and DE 2 264 429 A1 relates to a precision stamping press comprising two frame members rigidly connected to one another to which two table members for clamping two die parts are attached, the table members being able to move toward and away from one another axially along a hydraulic path. In the first frame member, there is a cylinder chamber in which two coaxial piston are disposed moveably relative to one another, the first piston being connected to a piston rod and the second surrounding the piston rod and forming a part of the first table member, which is moveably attached to the first frame member. The second piston has an internal threading and is screwed onto a sleeve that has external threads such that the axial position of the second piston can be adjusted.
DE 34 23 543 A1 further discloses a metal-processing press consisting of a bottom part and a working punch arrangement that can be moved axially away from the bottom part in the direction of the bottom part. The working punch arrangement comprises a primary punch and a secondary punch disposed substantially coaxially, the punches being able to move axially relative to one another, wherein the primary punch can glide axially in an axial penetration of the secondary punch.
EP 891 235 B1 discloses a precision blanking press with a hydraulically- or mechanically-driven ram having at least one hydraulic knife-edged ring and counterstay cylinder each. The knife-edged ring cylinder and the counterstay cylinder are disposed in a support cylinder that is held in constant contact with pressure pins by way of connection elements, wherein the support cylinder pushes the knife-edged ring piston to the lower starting position thereof at the end of the working stroke when the working force is suspended such that the pressure pins push out the punched grid. The knife-edged ring cylinder is kept in a cylindrical housing in a cross-beam, a knife-edged ring piston being guided in said housing and held, by a piston of the cylinder under pressure by the pressure medium, in a position that is in constant contact with the pressure pins.
In all of these known solutions, the knife-edged ring piston acts as the stripping/pushing element and the counterstay piston acts as the element that initiates ejection of the blanked part, the elements performing the stripping/pushing and ejecting with the same acting surfaces as in the displacing of the knife-edged ring piston/counterstay piston. This means that the stripping/pushing and ejecting is done using a piston of high mass, which leads to high forces occurring at the end stop when the piston is applied, the forces leading to undesirable impacts. Also, very high amounts of oil are needed for the high ejection speeds that are required, especially by large pumps in direct drives.
DE 10 2007 017 595 B3 further discloses a precision blanking press with an upper belt supported by side stands from below and disposed above the ram, and wherein the approach stroke of the ram occurs upwardly from below. The knife-edged ring cylinder and the counterstay piston comprise an outer piston and an inner piston having active surfaces of different sizes that can be pressurized together or individually, such that three different knife-edged forces and counterstay forces are generated under the same system pressure, wherein the common acting surfaces of the outer piston and the inner piston correspond to the total knife-edged ring force/total counterstay force and the acting surfaces of the inner piston correspond to the stripping/ejecting force. The knife-edged ring cylinder and counterstay cylinder volume displaced during the working stroke is conveyed to a pressure accumulator.
These known solutions do indeed make it possible to vary the stripping and ejecting force relative to the total knife-edged ring force, but the volume displacement continues to depend on the knife-edged ring piston such that adjustment of the stripping/pushing force and ejection force to match actual force requirements is not possible independent of the knife-edged ring force and the counterstay force. Also, the force in the knife-edged ring cylinder and counterstay cylinder must always be the same magnitude or greater than the pushing/ejection force, which limits applicability. The hydraulic circuit is complicated and expensive due to the controls within the knife-edged ring piston.
In light of this prior art, the object of the invention is to provide an apparatus and a method for stripping/pushing out a punched grid or internally formed part and for ejecting a blanked part from a die in a precision blanking press, wherein the force of stripping/pushing and ejection can be adjusted independent of the knife-edged ring force and the counterstay force while reducing the mass of the knife-edged ring and counterstay pistons, increasing the stripping/pushing-out and ejection speeds, and at the same time simplifying the hydraulic circuit.